1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition and, more particularly, to a radiation-sensitive resin composition suitable as a chemically-amplified resist useful for microfabrication utilizing various types of radiation, for example, deep ultraviolet rays such as a KrF excimer laser, ArF excimer laser, or F2 excimer laser, EUV, X-rays such as synchrotron radiation, or charged particle rays such as electron beams.
2. Description of the Background Art
In the field of microfabrication represented by fabrication of integrated circuit devices, photolithographic technology enabling microfabrication with a line width of 0.20 xcexcm or less has been demanded in recent years in order to achieve a higher degree of integration.
A conventional photolithographic process utilizes near ultraviolet rays such as i-line radiation. It is known in the art that microfabrication with a line width of a sub-quarter micron order using near ultraviolet rays is very difficult.
Therefore, use of radiation with a shorter wavelength has been studied for enabling microfabrication with a line width of 0.20 xcexcm or less. As radiation with a shorter wavelength, deep ultraviolet rays represented by a line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given. Of these, a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), and an F2 excimer laser (wavelength: 157 nm) have attracted attention.
As a radiation-sensitive resin composition applicable to shorter wavelength radiation, a number of compositions utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a photoacid generator which generates an acid upon irradiation (hereinafter called xe2x80x9cexposurexe2x80x9d) has been proposed. Such a composition is hereinafter called a chemically-amplified radiation-sensitive composition.
As the chemically-amplified radiation-sensitive composition, Japanese Patent Publication No. 27660/1990 discloses a composition comprising a resin containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. This composition utilizes the effect of the resin to release a t-butyl ester group or t-butyl carbonate group by the action of an acid generated upon exposure to form an acidic group such as a carboxylic group or a phenolic hydroxyl group, which renders an exposed area on a resist film readily soluble in an alkaline developer.
Micronization of photolithography processes in recent years has been remarkable. In particular, in the KrF photolithography processes the limit resolution has been decreasing close to one half of the light source wavelength or less. For this reason, characteristics required for photo resists have become increasingly stringent. In particular, improvement in the resolution performance, radiation transmittance, and surface smoothness of minute patterns, as well as a solution to the problem of partial insolublization during overexposure are desired.
For the improvement of resolution performance among these requirements, a method of increasing the amount of a photoacid generator which generates a super-strong acid upon exposure, a method of reducing the desorption energy of acid-dissociating functional groups in the resin, and the like has been proposed. The former method worsens the problem of partial insolublization during overexposure, whereas the latter cannot readily be put into practice due to difficulty in manufacturing the resin.
As a method for improving radiation transmittance, a method of increasing the content of (meth) acrylic-type recurring units in the resin and a method of decreasing the amount of photoacid generators are conceivable. However, the former method involves a problem of impairing heat resistance which results in lowered dry etching resistance, whereas the latter method has a problem of decreasing resolution performance.
A method of increasing the amount of photoacid generator and a method of decreasing the glass transition temperature of the resin are thought to be possible solutions to the improvement of surface smoothness of minute patterns. However, increasing the amount of photoacid generator results in a decrease in the radiation transmittance, which gives rise to trapezoid pattern configuration and difficult line width control during dry etching. Decreasing the glass transition temperature of the resin, on the other hand, impairs heat resistance. In view of this situation, development of a resist material or resist composition which can improve the resolution performance, radiation transmittance, and surface smoothness of minute patterns, and overcome the problem of partial insolublization during overexposure without adversely affecting basic characteristics of photoresists are strongly desired.
An object of the present invention is to provide a radiation-sensitive resin composition that responds to active radiation, for example ultraviolet rays such as a KrF excimer laser, ArF excimer laser, or F2 excimer laser, which when used as a chemically amplified resist can improve resolution performance, radiation transmittance, and surface smoothness of minute patterns, and overcome the problem of partial insolublization during overexposure without adversely affecting basic characteristics of a resist such as pattern form, dry etching resistance, and the like.
The present invention provides a radiation-sensitive resin composition comprising:
(A) a compound of the following formula (1), 
xe2x80x83wherein R1, R2 and R3 individually represent a hydrogen atom, a hydroxyl group, or a monovalent organic group, provided that at least one of the groups R1, R2, and R3 is a hydroxyl group, and R4 represents a monovalent acid-dissociable group or a monovalent organic group containing an acid-dissociable moiety in the structure,
(B) a resin comprising a recurring unit of the following formula (2), 
xe2x80x83wherein R5 represents a hydrogen atom or a monovalent organic group, Rxe2x80x2 represents a hydrogen atom or methyl group, n is an integer of 1-3, and m is an integer of 0-3, and
a recurring unit containing acid-dissociable group, the resin being insoluble or scarcely soluble in alkali, and
(C) a photoacid generator.
In a preferred embodiment of the above radiation-sensitive resin composition, R1, R2, and R3 in the formula (1) are individually a hydrogen atom, hydroxyl group, methyl group, ethyl group, methoxy group, or t-butoxy group.
In another preferred embodiment, R1, R2, and R3 in the formula (1) are individually a hydrogen atom or hydroxyl group.
In the above radiation-sensitive resin composition, R4 in the formula (1) is preferably a group of the following formula (3),
xe2x80x94CH2COOxe2x80x94R6xe2x80x83xe2x80x83(3)
wherein R6 represents a monovalent acid-dissociable group.
In the above radiation-sensitive resin composition, the recurring unit containing an acid-dissociable group in the resin (B) is preferably a unit obtainable by cleavage of a polymerizable unsaturated bond in a compound, which is obtainable by replacing the hydrogen atom in the phenolic hydroxyl group or carboxyl group in a compound selected from the group consisting of o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, p-hydroxy-xcex1-methylstyrene, and (meth)acrylic acid, with a monovalent acid-dissociable group.
In the above radiation-sensitive resin composition the introduction ratio of the acid-dissociable groups to the resin (B), which is the ratio of the number of the acid-dissociable groups to the total number of the unprotected acidic functional groups and the acid-dissoclable groups in the resin, is preferably 10-50%.
In the above radiation-sensitive resin composition the photoacid generator (C) preferably comprises a compound of the following formula (4), 
wherein R 7 is a monovalent organic group and R8 is a divalent organic group.
Other objects, features and advantages of the invention will hereinafter become more readily apparent from the following description.